The present invention, in some embodiments thereof, relates to system and method for detecting traces of chemical substances and, more particularly, but not exclusively, to system and method for detecting traces of chemical substances in a stream of gas.
Detection of molecules of organic and nonorganic chemical substances and/or compounds in gas samples is required for various applications, for example scientific applications, manufacturing process applications, and homeland security applications.
Several types of machines have been developed to detect trace signatures for chemical substances. A common technology for this application is ion mobility spectrometry (IMS). This method is similar to mass spectrometry (MS), where molecules are ionized and then moved in an electric field in a vacuum, except that IMS operates at atmospheric pressure. The time that it takes for an ion, in IMS, to move a specified distance in an electric field is indicative of that ion's size to charge ratio: ions with a larger cross section will collide with more gas at atmospheric pressure and will therefore be slower. Gas chromatography (GC) is often coupled to the detection methods in order to separate molecules before detection. This improves the performance of the chemical detecting unit and adds another dimension of data, as the time it takes for a molecule to pass through the GC may be used as an indicator of its identity. GC normally requires a bottled inert gas and GC columns.
During the last years, various systems and methods having high sensitivity for detecting traces of chemicals carried in the ambient air have been developed. Some of the systems and methods have an improved velocity since many of the applications prefer a complete analysis to be completed in less than a minute. These developments allow detecting the presence and/or the absence of one or more chemical substances by analyzing air samples and detecting trace concentrations in less than a minute. For example, U.S Patent Application Number 2008/0250877, published on Oct. 16, 2008 describes a sample collection method that releases and collects residues of explosives and other chemicals from a surface. This method is implemented into a compact detection system that can be used as a “wand” for screening chemicals residues on a subject. The wand configuration includes multi-function for sampling and detecting multiple threads. The invention further describes a method of inspecting a subject using an interrogating apparatus in a sweeping motion; the near range closed loop particle sampling arrangement allows effective collection of particle and vapor residues from a targeted surface. The invention also describes a sampling and detecting apparatus for on-the-fly threat detection using compact ion mobility based detectors.